How many layers can I make in Blender 2.8
There are no more layers in Blender 2.80. Layers have been replaced by Collections
I have no idea, how many of them you can create (the limit might even be your hardware here), but it is basically as many, as you wish. 

If you create a new text block in the Text editor, type:

import bpy 

for i in range(1,1000):
    C = bpy.data.collections.new("Collection"+str(i) )
    bpy.context.scene.collection.children.link(C)


and then hit Run Script, it will create 1000 empty collections. If you need that many, or if you start to worry about collection amount limitations chances are you are doing something very wrong. Don't worry about them.